The United States Federal Aviation Administration has reaffirmed the airworthiness of the Boeing 737 MAX in the wake of the Ethiopian Airlines crash that killed 157 people. It comes after several countries and airlines grounded the aircraft.

There have been mounting concerns about whether Boeing’s best-selling single-aisle airliner is safe to fly, after crashes in Indonesia last October and in Ethiopia last week that dealt a heavy blow to its reputation. In a statement on Monday, the FAA said that, while “external reports are drawing similarities” between the accidents, which killed 346 people in total, it’s too early to judge if a common issue is to blame.

“This investigation has just begun and to date we have not been provided data to draw any conclusions or take any actions,” the agency said.

While the FAA opted to proceed with caution, aviation authorities in China, Indonesia and Ethiopia, have rushed to ground their respective fleets of the US aircraft manufacturer’s most popular plane, as a precaution.

Stock markets have also been reacting to Boeing’s woes, its shares sliding more than 5 percent on Monday.

With no definite conclusions reached from last October’s Lion Air crash yet, let alone last week’s Ethiopian Airlines disaster, speculation has been rife, with some experts suggesting that a common technical fault had doomed both planes.

What do the incidents have in common?
Desmond Ross, aviation security expert, former pilot and CEO of DRA consultancy, told RT that, although a complete set of data is not available on either of the crashes, “they do look very similar.”

There have been damning reports that the Ethiopian jet had experienced a violent nosedive shortly after departing from Addis Ababa airport this week, and that this incident was “possibly caused by similar issues to that of the … Lion Air crash.”

The brand-new jet is marketed as more fuel-efficient and technically superior to its direct competitor, the Airbus A320neo family. To beat the European jet, Boeing had installed larger engines that were moved a bit further forward, tilting the balance of the aircraft. To compensate for this, the company altered on-board software and the flight control system, Ross explained.

What makes the 737 MAX particularly (un)safe?
The MAX-series jet has not yet become the world’s most dangerous plane to fly. Other models, like the de Havilland Comet, the first commercial plane, or Tupolev Tu-154, the working horse of Soviet civil aviation, had poorer safety records. But allegations quickly spread that the Lion Air crash last year could have been prevented had Boeing tackled the technical glitch.

Nevertheless, shortly after the incident Boeing released an update to pilots flying the 737 MAX airliner, warning of the issue. But it could be that some pilots “have not been properly briefed or properly trained,” Ross speculated.

Meanwhile, Alexey Kochemasov, a Boeing 737 captain at Russia’s Pobeda airline, said it’s too early to say if the same system played a role in both incidents. The 737 is a reliable plane and everything a pilot should know to tackle the problem “was written up clearly” in Boeing’s safety directive. Kochemasov warned against drawing parallels between the two cases before getting the results of relevant studies and expert analyses.

Boeing goes into damage control
Boeing CEO Dennis Muilenburg sought to brush off speculation about the similarities between the two crashes and to reassure staff that it is working hard to discover and fix the underlying issue, if any.

“While difficult, I encourage everyone to stay focused on the important work we do. Our customers, business partners and shareholders depend on us to deliver for them,” Muilenburg wrote, adding that the company would be “further strengthening the support”to the “737 team.

In the letter to employees that circulated on social media shortly after the FAA announcement, Muilenburg argued that “speculating about the cause of the accident or discussing it without the necessary facts is not appropriate and could compromise the integrity of the investigation,” while highlighting the company’s vast output and its impressive track record of having delivered “more than 370 737 MAX airplanes to 47 customers.”

While Muilenburg preaches optimism in the face of trouble, others predict more financial and reputational setbacks for the aviation giant.

The outcomes of the Ethiopian disaster could become even more painful “if the results of the investigation turn out to be negative,” Ross predicted. “I know quite a few people who are selling the shares of Boeing as we speak and they’re getting out of any investment in the Boeing company,” he revealed.

Kochemasov, on the other hand, argued that the company would emerge relatively unscathed: saying that its reputation will be damaged “is like saying that three Mercedes cars crashing in one day will damage reputation of Mercedes company,” he believes.